Adult intestinal epithelium is composed of a monolayer of rapidly proliferating and differentiating cells. Throughout this continuous process of proliferation/differentiation, a remarkable degree of spatial complexity is maintained. Little is known about molecular mechanisms that underlie development and maintenance of this geographic differentiation. Previous studies have utilized transgenic mice to functionally map cis-acting elements that regulate expression of liver (L-) and intestinal (I-) fatty acid binding protein (FABP) genes in gut epithelium. Both L-and I-FABP genes have maximal expression in proximal small bowel beginning in late fetal life. These data imply that different cis-acting elements regulate expression in proximal vs. distal gut. This proposal will focus on another member of the fatty acid binding protein family, ileal lipid binding protein, that is also expressed in small bowel epithelium; however, in contrast to other FABPs the ileal protein is only expressed in distal small bowel and induction of gene expression occurs at the suckling/weaning transition phase. Portions of the 5' nontranscribed domain of the mouse ileal protein' gene will be linked to a reporter - human growth hormone gene - and the pattern of transgene expression in transgenic mice will be determined by RNA blot hybridization and immunocytochemical methods. Sequence analysis will compare/contrast the 5' non-transcribed domains of ileal protein, L- and I-FABP genes. Developmental studies will be performed to focus on cis-acting elements that regulate induction of the mouse ileal protein gene at the sucking/weaning transition, a critical period of gut development. These studies should provide better understanding of mechanisms that regulate gene expression in developing and adult gut.